A commercial AHU can be a reasonable candidate for a fan-wall retrofit, but an attractive array picture cannot answer the project question by itself. The decision is whether the complete cabinet can deliver the required air service, fit safely, respond to a module fault and improve measured input under a fair before-and-after comparison. This article uses a case-study method; it does not report a measured installation or a named customer’s result.
Practical decision: survey the existing unit and write down the measurement boundary before selecting fan cells. If the current airflow, pressure path, operating schedule or cabinet geometry is unknown, collect that information first. No universal fan count, energy-saving percentage, payback or fault tolerance follows from the word “FanGrid.”
Define the service before choosing an array
Begin with the ventilation, temperature, humidity and operating-hours requirements of the space served. Record the present AHU airflow and the pressure it must overcome at the relevant operating points. An old nameplate or motor rating is not a substitute for a measured duty point: filters may be loaded, dampers may be partly closed and the occupied schedule may differ from the original design.
Write down the acoustic limit, available electrical supply, control interface and acceptable interruption during installation. If continuity matters, describe exactly what the unit must do with one module stopped. Calling an array “N+1” before defining that duty and testing it is only a label.
Survey the full air path and the real cabinet
The fan works inside a system. Note the filters, coils, dampers, silencers, transitions and duct restrictions on both sides of the fan section. Measure the usable width, height and depth, plus door clearance and the path for lifting equipment into place. Check where a sealed bulkhead, service access and electrical distribution could fit. A layout that fits in a rendering may still block maintenance access or leave air bypassing the cells.
The LONGWELL FanGrid solution presents a modular EC plug-fan array as one family option. The rendering below helps identify the repeated cells and frame. It is an illustration of architecture, not a photograph of this AHU, a verified module count for a project, or evidence of airflow, noise, energy or redundancy.
Size parallel fans at a common pressure
For fans in parallel, compare each active cell’s airflow at the same pressure, then assess the combined array against the AHU system resistance. Do not multiply a free-air airflow figure by the number of cells and treat it as installed capacity. The mounting frame, plenum, guard, bulkhead and nearby surfaces can change the effective duty. The fan curve and the system curve need to meet at the required operating point.
LONGWELL lists EC plug fans as a product family. A family page establishes that such modules are offered; it does not select an exact model or prove this cabinet’s fit. Ask for the current curve and drawing of the proposed exact model and suffix, then check voltage, control, sound and mounting details against the actual AHU. The company’s fan-wall design guide expands on the array-versus-system distinction.
Make installation and controls part of the design
The retrofit is more than replacing a rotating part. Plan a sealed support structure, cable routing, protective devices, safe isolation and a service procedure for each module. Confirm that the existing casing can carry the new assembly and that the intake and discharge spaces remain usable. Cabinet alteration and electrical work require the AHU owner and qualified installers to approve the actual design.
Define the control sequence before ordering: start and stop, speed demand, pressure sensing, alarms, restart after power loss and what happens when one fan or controller is unavailable. An array can contain several independently driven fans while still depending on one shared sensor or control path. The failure behavior has to be designed and witnessed, not inferred from the number of impellers.
Use one equal boundary for before-and-after claims
An energy comparison is meaningful only when both configurations provide the same required service. Record airflow, static pressure, filter state, occupied schedule and the measurement location before the change. After commissioning, repeat at the same agreed boundary and note any changes to filters, dampers, setpoints or occupancy. Measure electrical input at a stated boundary, such as the incoming supply to the complete fan system, rather than comparing one old motor reading with an incomplete new-system reading.
If those baseline records do not exist, describe the expected mechanism and proposed test plan without promising a percentage. The brochure’s indicative savings and payback figures are not a substitute for a controlled record for this building.
Commission normal and one-module-out operation
Commission the installed array as part of the whole AHU. Confirm rotation, direction of airflow, stable controls, total delivered airflow, pressure, electrical input and sound at the agreed points. Check that each fan reports its state correctly and that the alarm reaches the operator. Then stop one module under a controlled procedure and record whether the remaining equipment meets the specified reduced or full duty without exceeding its permitted operating range.
The result may show full continuity, a documented reduction in airflow or a need to revise the design. Each is a valid engineering finding; none should be replaced with a generic “N+1” statement. Keep the as-built drawing, settings, curves, commissioning sheet and maintenance access instructions with the AHU handover record.
What to send for a useful engineering review
Send the AHU drawing and photos, current fan details, airflow and static-pressure requirements, filter and coil schedule, measured baseline, operating hours, available electrical supply, control protocol, sound limit, space and access constraints, and the precise one-module-out duty. Those inputs let an engineer decide whether a fan wall is appropriate and which exact modules deserve a curve and fit review. If a different fan arrangement meets the service more simply, the same evidence will make that clear.
For a scoped LONGWELL review, email sales@longwellfans.com with the AHU information and the duty you need to verify.
